Automatic braking system for trains



May 21, 1968 AKIRA WATANABE ET AL AUTOMATIC BRAKING SYSTEM FOR TRAINS Filed Aug. 4, 1965 F'IG.I

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A A tvDCB fime 1 W1 V/l Wt Hme &MWM [M I VEN'TORS BY WI M United States Patent 3,384,744 AUTOMATIC BRAKING SYSTEM FOR TRAINS Akira Watanabe and Kciichi Hayashi, Tokyo, Japan, assignors to Tokyo Shibaura Electric (10., Ltd), Kawasakishi, Japan, a corporation of Japan Filed Aug. 4, 1965, Ser. No. 477,253 4 Claims. (Cl. 246-182) ABSTRACT OF THE DISCLOSURE An automatic braking system for a train comprising a braking device, a receiving means mounted on said train to successively receive signals from a number of spaced signal transmitters installed along a railway track, a first logical circuit device connected to receive output signals from said receiving means to actuate said braking device to maintain the speed of said train at a predetermined value and a second logical circuit device also connected to receive the output signals from said receiving means to actuate said braking device in response to a speed which is higher than said predetermined value.

This invention relates to an automatic braking system for trains and more particularly to an automatic braking system for high speed electric trains.

With recent trend of high speed running of trains it has become difficult to control the operation of trains relying upon the judgement of the drivers or motor men. As a result a system of automation operation of trains has been developed including a number of pattern signal generators located along the railway track and an apparatus mounted on a train to receive said pattern signals to control the train according to the predetermined command or running pattern. With this system not only the burden of the driver was greatly reduced but also the train can be automatically controlled to run safely so that he is only required to give a command to an automatic train control device at the time of starting or to supervise this control system. In such an automatic train control device it is most essential to operate the train safely. Thus, for example, if the train is running at a speed above that determined by the command transmitted from the ground, or the predetermined pattern, it would be impossible to stop it at the predetermined point or station when brake is applied in a prescribed manner, thereby causing such dangers as over run and collision. Thus, it will be seen that an automatic braking control system or device constitutes an important element to the automatic running of a train of the type described above. As long as the train passes by a predetermined point at a predetermined speed its automatic braking control system will operate to maintain the braking device in the released condition but when the speed of the train is above the predetermined speed the automatic braking control system will actuate the braking device to reduce the train speed. When a fault occurs, for example, on the ground that the control system fails to respond to the command, dangerous runaway will be resulted.

An object of this invention is to provide a novel automatic braking device for trains which can prevent such dangerous accidents.

Another object of this invention is to provide an auto- 3,384,744 Patented May 21, 1968 "ice matic control system which can safely decelerate and stop a train at a predetermined point.

Briefly stated this invention can be practiced by providing an automatic braking system comprising a braking device, a receiving means mounted on a train to successively receive signals from a number of spaced signal transmitters installed along a railway track, a first logical circuit device connected to receive output signals from said receiving means to actuate said braking device to maintain the speed of said train at a predetermined value and a second logical circuit device also connected to receive the output signals from said receiving means to actuate said braking device in response to a speed which is higher than said predetermined value. Thus under normal conditions the train will be controlled by the first logical circuit device to follow a prescribed running speed pattern whereas should any fault arise in the first logical circuit device or in any control apparatus associated therewith the train would be safely decelerated and stopped at or close to a predetermined point under the control of the second logical circuit device.

The novel features of the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. However, the invention, both as to its organization and operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the drawings wherein:

FIG. 1 shows a block diagram of one example of an automatic train braking system of this invention;

FIG. 2 shows a graph illustrating curves useful to explain the operation of this invention;

FIG. 3 shows a connection diagram of one example of a logical circuit device utilized in the automatic train braking system of this invention;

FIG. 4 shows one example of an energizing circuit of an electromagnetic valve of a train; and

FIGS. 5 and 6 show various voltage curves to explain the operation of the circuit shown in FIG. 3.

While in the following a preferred embodiment of this invention as applied to an electric train or an electric car will be described in detail it should be understood that the invention can equally be applied to any other type trains, and that powering control of the train is provided by any suitable control apparatus which responds to speed command signals transmitted thereto from ground. Referring firstly to the block diagram shown in FIG. 1 a train or car 10 is equipped with a suitable braking device 11 such as a pneumatic or an electropneumatic brake. As will be described in more detail hereinafter the braking device 11 is arranged to be controlled in response to the output signals from a signal receiver 12 mounted on the car 10. A number of signal transmitters 13 are installed along a railway track which may comprise a number of inductive windings spaced along the track to transmit electromagnetic signal waves of about 7.5 kc. or 9.5 kc. per second. Although the purpose of these inductive coils will be described later, they are installed along the track with spacings proportional to the speed of a train running between stations at a prescribed schedule. So long as the train is correctly running according to the prescribed running schedule commands of a definite period will be supplied to the receiver 12 no matter what point the train is passing by. As diagrammatically shown, the receiver 12 is provided with two output terminals, one of which being connected to a first logical circuit device 14 which logically determines whether or not the train is running at a predetermined speed to produce an output. This output is applied to an electropneumatic translating device or a means 15 for translating an electric quantity to pneumatic pressure in a braking system, the output therefrom being applied to the braking device 11. The other output terminal is connected to a second logical device 16 which responds to a train speed exceeding the set value of said first logical circuit device 14 to produce an output to operate the braking device 11 through an electromagnetic valve 17.

The circuit constructions of the receiver 12 and of the logical means 16 will now be considered by referring to FIG. 3. As shown, the receiver 12 is constituted by a signal inductance coil which functions to receive said electromagnetic signal waves to apply them to an amplifier 18, the output therefrom being connected to a tuning circuit 20 through a coupling transformer 19. As already has been pointed out, as the received signals are of a periodic form the tuning circuit will exhibit periodically tuning conditions and the output from the tuning circuit 20 is applied across a potentiometer resistor 22 through a half wave rectifier 21 acting as a detector. An intermediate tap of the resistor 22 is connected to a base electrode of a PNP transistor 24 through a resistor 23. The lower terminal 25 of the resistor 22 is connected to a DC terminal 25 of plus 20 volts, for example, and the collector electrode of the transistor 24 is connected to a DC terminal 27 of minus 20 volts, for example, through a relay winding 28 and a resistor 26. Due to the switching operation of the transistor 24 the current flowing through the relay coil 28 is interrupted to produce an oscillation, so that a condenser 29 is connected in parallel with the relay 28 to smooth out the relay current. The collector electrode of the transistor 24 is also connected to the ground through a resistor 129 and a condenser 30, the nongrounded terminal thereof being connected to one terminal of a pten tiometer resistor 35 through a plurality of serially connected resistors 31, 32, 33 and 34. The other terminal of the potentiometer resistor 35 is grounded through a relay 36. Respective common junctions between resistors 31 to 34 inclusive are grounded through condensers 37, 38 and 39 whereby to constitute a filter circuit 40. A Schmidt trigger circuit 60 including a pair of PNP transistors 41 and 42 is provided with the emitter electrodes of both transistors grounded through a common resistor 43. Collector electrodes of the transistors 41 and 42 are connected to a DC terminal 46 of minus 20 volts, for example, respectively through resistors 44 and 45. The base electrode 41 of the transistor 41 is connected to an intermediate tap of the potentiometer resistor 35. Further, the collector electrode of the transistor 41 is connected to the base electrode of the transistor 42 through a parallel combination of a condenser 48 and a resistor 49. Further, a PNP transistor 52 is provided having a collector electrode connected to the base electrode of the transistor 41 through a resistor 50 and an emitter electrode connected with the base electrode of the transistor 42 through a resistor 51. Alternating current is supplied across the base and emitter electrodes of the transistor 52 from an AC source 54 via a transformer 53. The transistor 52 acts as a chopper in a manner to be described later. The output from the Schmidt trigger circuit 60 is derived from the collector electrode of the transistor 46 and is applied to an amplifier 55. The output of the amplifier 55 derived out through a transformer 56 is rectified by a full wave rectifier 57 and is then applied through a filter to a relay 58 which actuates the braking device. Normal open contacts 28 and 36 of the above mentioned contacts 28 and 36,, respectively are included in circuit with the relay 58.

It is to be understood that when the relay 58 is energized, the braking force is removed and vice versa. This arrangement is especially useful for automatic train braking systems because whenever the relay 58 becomes deenergized owing to a fault of any portion of the receiver 12 and the logical circuit device 16, brake will be applied. FIG. 4 shows an energizing circuit for the electromagnetic valve 17 shown in FIG. 1, which is controlled by a normally opened contact 58,, of the relay 58 of FIG. 3. When the contact 58 is opened in response to the deenergization of the relay 58 the electromagnetic valve 17 will operate to actuate the braking device and vice versa.

While it is possible to safely operate a train by controlling it by the output from the logical circuit device 16, its response is sluggish and hence it is unable to control the train at high accuracy since, as shown in FIG. 3, the logical circuit device 16 includes a number of condensers 37, 38 and 39 as its components. According to this invention these difiiculties are eliminated by providing an additional logical circuit device having quick response property and hence can provide accurate control whereby to use said first logical circuit device 1 6 to control the train only when the additional logical circuit device 14 gets out of order.

The operation of this system is as follows:

Referring firstly to FIG. 3 the base electrode of the transistor 24 is normally biassed by a positive potential supplied from the terminal 25 to maintain it in the off condition. As a train runs the receiver 12 will receive successive electromagnetic signal waves sent from the ground to operate the tuning circuit 20. Thus periodically detected output signals are applied across the potentiometer 22 via the rectifier 21 having :such polarity as to bias negatively the base electrode of the transistor 24, thus periodically turning it on and off. When the transistor 24 is off, the condenser 30 will be charged from the minus 20 volt source 27 through resistors 26 and 29, whereas when the transistor is on, the condenser 30 will discharge through the resistor 129 and the collectoremitter path of the transistor 24. The time constant of the charging circuit is determined mainly by the values of resistors 26 and 27 Whereas that of the discharge circuit is by the resistor 29 alone. As a consequence, it the resistor 26 is designed to have a value sufficiently larger than that of the resistor 29, the charging time constant would be large whereas the discharge time constant small. FIG. 5a represents the terminal voltage of the condenser 30 and FIG. 5b represents the base electrode voltage of the transistor 24. As can be easily understood from FIG. 5 the condenser voltage builds up during the periods wherein the signals from the ground are absent but upon receipt of the signals the condenser will discharge immediately to decrease its terminal voltage to zero. Thus, the voltage across the condenser varies periodically in response to the periodic signals supplied from the ground. The condenser voltage having a wave form as shown in FIG. 5a is smoothed by the action of the CR filter 40 to provide a unidirectional voltage as shown by V in FIG. 5a, which is applied across the potentiometer 35. Since either one of the transistors 41 or 42 of the Schmidt trigger circuit 60 is normally conductive a constant voltage is maintained across the resistor 43. This voltage serves as a reference voltage for the base electrode of the transistor 41. The voltage determined by the position of the tap of the potentiometer 35, or the voltage V FIG. 5a, is compared with said reference voltage to provide a difference voltage applied to the base electrode of the transistor 41. The base electrode of the transistor '41 in the-Schmidt trigger circuit 60 is connected to a DC terminal 59 of plus 20 volts, for example, via the transistor 52 which is controlled to effect periodic switching by a voltage supplied from an AC source 54. Accordingly, during the period wherein the positive voltage of the -DC terminal 59 is applied to the base electrode of the transistor 41 the transistor is maintained in its off state even when said difference potential is applied to the base electrode. If this difference voltage is applied in such a manner as to 'bias negatively the base electrode of the transistor 41 during hal-f cycles of alternating current in which the transistor 52 is maintained off, the transistor 41 will become on. In response to conduction of the transistor 41, the transistor 42 will become otf and vice versa. Thus, the transistor 52 acts to interrupt the input to the transistor 41, thus providing an alternating current. It will be obvious that the Schmidt trigger circuit 60 effects switching operation only when the voltage derived from the potentiometer 35 is larger than that across the resistor 43, and the Schmidt trigger circuit 60 ceases its switching operation when the voltage derived from the potentiometer 35 becomes smaller than that appearing across the resistor 43. The output of the Schmidt trigger circuit 60 which is derived out through the collector electrode of the transistor 42 is supplied to the transformer 56 through the amplifier 55. Thus, an AC output will appear on the secondary side of the transformer 56 only when the fractional voltage obtained from a potentiometer 35 is larger than that appearing across the resistor 43, whereas no output will appear on the secondary side of the transformer 56 when the fractional voltage from the potentiometer 35 is smaller than that of the resistor 43 since, under this condition, a DC output is supplied to the amplifier 55 from the Schmidt trigger circuit 60.

As has been pointed out a number of electromagnetic inductance coils are installed along the railroad at spacings proportional to the schedule speed of a train. As a consequence so long as the train is correctly operated to pass by a predetermined point at a prescribed speed, the receiver 12 will receive signals of equal spacings or periods. Thus, under normal operating condition the voltage impressed across the potentiometer 35 or the voltage V shown in FIG. 5a is constant. If, under this condition, the fractional voltage of the potentiometer 35 were selected to be larger than that of the resistor 43 an AC output would appear on the secondary side of the transformer 56. As long as the transistor 24 continues to repeat its on-off operations the relay 28 will be energized continuously to close its contact 28 In other words, while the train is running the contact 28 is maintained closed. When the value of the voltage V exceeds a predetermined value, the relay 36 will operate to close its contact 36,,. As a result the relay 58 will be connected to the secondary winding of the transformer 56. When the speed of a train exceeds a predetermined running speed the spacing between signals received by the receiver 12 will be reduced as shown in FIG. 6b, thus decreasing the charging period available for charging up the condenser 30 to decrease its terminal voltage as well as the mean voltage V to be applied across the potentiometer 35, as shown in FIG. 6a. This results in the application of a positive voltage to the base electrode of the transistor 41 included in the Schmidt trigger circuit 60 to cause it to provide a direct current output, thus removing output from the secondary of the transformer '56. As already mentioned deenergization of the relay 58 will result in the application of brake.

FIG. 2 shows scheduled speed curves with the abscissa representing the distance between two adjacent stations and the ordinate the train speed wherein a curve 61 repre sents a schedule speed curve when the train is controlled by the logical circuit device 14 whereas a curve 62 that of the train when it is controlled by the logical circuit device 16 shown in FIG. 1. If it is assumed that the origin 0 represents the starting station, the train will generally be controlled to operate along the curve 61 to arrive at the next station represented by a point S. However should any fault occur in the logical circuit device 14, or in the electropneumatic translating device and the like shown in FIG. 1, at a point A, thus becoming unable to operate the braking device 11, the deceleration control otherwise beginning from the point A will not take place but the train will tend to maintain constant speed as shown by a straight line 61'. Consequently the train will pass by the point S at a substantially high speed. However, when a point B is reached where curves 61 and 62 cross each other the output from the logical circuit device .16 will disappear to actuate the braking device 11 as has been fully described in connection with FIG. 3. In this case, if the braking force is applied relatively slowly or at a prescribed rate, the train would be decelerated along the curve 62 to stop the train at a point S slightly beyond the predetermined point or station S. On the contrary if a quick brake is applied at said point B on the curve 62 the train could be stopped at a point S" a little short to the predetermined point S. Thus by suitably setting the braking effect beforehand it is easy to stop the train at or close to the predetermined point S.

As will be clearly understood from the foregoing description, this invention provides a novel automatic braking system which can safely decelerate a train to stop it at or near a predetermined station even when a logical circuit device which normally controlls the automatic braking system gets out of order.

While the invention has been described in terms of an electric train it should be understood by those skilled in the art that the invention can also be equally applied to any type of trains. It is further to be understood that many changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An automatic braking system for a train comprising a braking device,

a number of spaced signal transmitters installed along a railway track at spacings proportional to the programmed running speed of the train,

a receiving means mounted on the train to successively receive signals from said signal transmitters as the train advances,

a first logical circuit device receiving output signals from said receiving means to actuate said braking device to make the period of said signals maintain a constant value determined by said programmed speed, and

a second logical circuit device receiving output signals from said receiving means to respond to a predetermined speed higher than said programmed speed maintained by said first logical circuit, said second logical circuit device including a frequency-voltage converting circuit to obtain a DC voltage inversely proportional to the period of the output signals of said receiving means, a comparison circuit consisting of a Schmidt circuit comparing said DC voltage with a reference voltage determining said predetermined speed to produce an AC output excited by an AC signal when said DC voltage is higher than said reference voltage and a predetermined DC output when said DC voltage is lower than said reference voltage, and a relay responding only to said AC output from said comparison circuit to control said braking device.

2. The automatic braking system for a train according to claim 1, wherein said frequency-voltage converting circuit comprises a switching transistor rendered on and 011 by the output signals from said receiving means, a capacitor charging and discharging circuit charged by a given source of supply at a time constant and discharged through conduction of said transistor, and a filter circuit smoothing the terminal voltage of said capacitor.

3. The automatic braking system for a train according to claim 2, wherein there is provided a relay energized by the output of said switching transistor, of which a normally open contact is incorporated in series with a coil of a relay controlling said braking device.

4. The automatic braking system for a train according to claim 2, wherein there is provided a relay energized by the output of said filter circuit, of which a normally open controlling said braking device.

7 8 contact is incorporated in series with said coil of said relay 3,270,199 8/ 1966 Smith 246-182 3,300,639 1/ 1967 Bowman et a] 246182 References Cited FOREIGN PAFFEINTS UNITED STATES PATENTS 5 806,625 12/ 1958 Great Bntam.

10/ 1955 MaeIlPaa et 5 -3 ARTHUR L. LA POINT, Primary Examiner.

12/1959 Hughson 46 8 Hughson T- Examlner.

8/1966 Hayashi et a1. 246182 

